ACR + MCP: Complementary Layers

The Relationship

MCP (Model Context Protocol) defines the wire protocol — how agents discover and call tools. It’s the plumbing. Standardized, well-adopted, essential.

ACR (Agent Capability Runtime) manages what goes into the agent’s context window — which capabilities are loaded, at what resolution, with what budget. It’s the OS layer on top of the plumbing.

They solve different problems:

Concern	MCP	ACR
Tool discovery	✅ Server listing	❌ Not its job
Tool execution	✅ JSON-RPC	❌ Not its job
Context budget	❌	✅ LOD, eviction, promotion
Dynamic loading	❌	✅ Triggers, mount/unmount
State persistence	❌	✅ Serialize across eviction
Multi-resolution	❌	✅ index/summary/standard/deep

Why MCP Needs ACR

MCP tells the agent what tools exist. But MCP doesn’t answer:

Which tool instructions should be in context right now? An agent with 50 MCP tools doesn’t need all 50 instruction sets loaded. ACR provides LOD-based loading — full instructions for active tools, one-liners for the rest.
What happens when context gets full? MCP has no concept of context pressure. ACR manages budget, evicts low-priority capabilities, demotes resolutions, and preserves state across eviction.
How do tools compose? MCP tools are independent endpoints. ACR capabilities declare dependencies, co-activation rules, and provide/require contracts.

Integration Points

MCP Tools → ACR Capabilities

An ACR capability can wrap one or more MCP tools:

name: linear
requires:
  tools:
    - mcp-linear-create
    - mcp-linear-search
    - mcp-linear-update

When the linear capability is mounted, ACR ensures:

The right MCP tool instructions are in context
At the right resolution level
Within budget
With state restored from last session

ACR as Context Manager for MCP Deployments

For agents with many MCP servers, ACR provides the missing orchestration:

Cold start: Register all MCP tools as ACR capabilities at index level (~10 tokens each)
Active use: When a user mentions a topic, triggers promote relevant capabilities
Budget pressure: Evict least-relevant tool instructions, keeping state
Session end: Serialize tool state for next session

Without ACR, agents load all MCP tool instructions at once — burning context budget on tools they may never use.

The Vision

MCP standardizes the wire. ACR standardizes the context. Together, they give agents:

Discovery (MCP) + Relevance (ACR): Know what tools exist AND which ones matter right now
Execution (MCP) + Instructions (ACR): Call tools AND know how to use them well
Connection (MCP) + Memory (ACR): Connect to services AND remember state across sessions

ACR is not a replacement for MCP. It’s the layer that makes MCP-equipped agents smarter about what they load, when they load it, and how they manage the finite resource of the context window.